The present invention relates to a pipe end preparation tool having improved torque reacting and clamping capabilities in order to minimize the time necessary to machine pipe ends.
Portable lathes for machining the ends of pipes are well known in the art and typically comprise a mandrel, a device to clamp the mandrel to the pipe such that it is aligned with the center line of the pipe and a power unit mounted on the mandrel. The power unit has a rotatable portion, to which one or more machining tools are attached, and a non-rotatable portion slidably attached to the mandrel. Means are provided on the power unit to move it axially along the mandrel in order to feed the machining tools into the end of the pipe.
The power unit also comprises a drive mechanism, attachable to an external power source, to rotate the rotatable portion to which the machining tool is attached. Typically, a pneumatically or hydraulically driven motor is attached to the power unit such that its output shaft is drivingly connected to the rotatable portion. The drive may include inter-engaging bevel gears, one such bevel gear attached to an input shaft, while the meshing bevel gear is affixed to the rotating portion of the power unit.
Clamping means are provided on one end of the mandrel to clamp it to the pipe. Such clamping means may be either external, to clamp the mandrel to the exterior of the pipe, or internal, wherein a portion of the mandrel extends into and is clamped to the interior of the pipe. The internal clamping devices typically comprise a plurality of clamping members mounted on the mandrel so as to move in a radial direction with respect to the longitudinal axis of the mandrel. The clamping members are radially expanded or contracted by axial movement between wedge surfaces formed on a portion of the mandrel and each of the clamping members. Such clamping members are usually formed as narrow, elongated members having a significant length in the direction of the longitudinal axis of the mandrel.
In order to minimize the time for machining the end of an elbow or a pipe, it is necessary to take as large a cut per revolution of the machining tool as possible. The torque necessary to maximize the cut must be reacted by the interconnection between the non-rotatable portion of the power unit and the mandrel, as well as through the device clamping the mandrel to the elbow or pipe. Torque reacting devices are known which are designed to be interposed between the mandrel and the power unit housing to increase their torque reacting capabilities. However, such devices are subject to shear forces and wear which require them to be replaced, since they are not adjustable to accommodate for such wear.
Elongated clamping members do not provide satisfactory results even when the mandrel is attached to an elongated pipe section in which there is sufficient room within the interior of the pipe to accommodate the length of the clamping members. The relatively narrow dimension of the known clamping members does not provide the necessary clamping force to react the torque generated during maximum cut machining operations.
Problems also arise when the mandrel must be attached to a pipe elbow or the like, since there is usually not room within the interior to accommodate the length of the elongated clamping members. Such known clamping devices have failed to provide the necessary rigid support to the mandrel to accurately machine the ends of the elbow.